This invention is based in part on the elucidation of new structural conformations and functions of the sodium/potassium adenosine triphosphate synthase (Na/K ATPase), and especially elucidation of new binding sites and interactions. The present invention provides applications of surprising structural and functional relationships between Na/K ATPase and compounds which interact with Na/K ATPase. The invention provides solutions to chemically affecting not only the Na/K ATPase interactions, but also regulators known to be upstream and downstream.
Sodium and potassium transport activity across the cell membrane is intrinsically related to many cellular processes including metabolism, gene expression and cell growth. The Na/K-ATPase is highly expressed and represents one of the most fundamentally important proteins of animal physiology. Moreover, the expression and the activity of Na/K-ATPase are important in regulation of the overall transport activity of a cell. This so-called pump/leak coupling exists in almost every mammalian cell. Because protein phosphorylation constitutes a pivotal mechanism by which the cellular processes are coordinated, the inventors postulate the existence of a receptor mechanism that can couple the transmembrane transport activity of Na/K-ATPase to on/off of protein kinases.
It is known that a large number of Na/K-ATPase interacts directly with Src kinase in cultured cells as well as in vivo. The interaction involves at least two pairs of protein domains. Specifically, the second cytosolic domain of α1 subunit (CD2) interacts with the Src SH2 and the nucleotide binding (N) domain associates with the Src kinase domain. The latter interaction keeps Src in an inactive state and binding of cardiotonic steroids such as ouabain to the Na/K-ATPase/Src complex activates the associated Src, resulting in the assembly and activation of various protein kinase cascades.